[WebAssembly] Don't fold frame offset for global addresses

When machine instructions are in the form of
```
%0 = CONST_I32 @str
%1 = ADD_I32 %stack.0, %0
%2 = LOAD 0, 0, %1
```

In the `ADD_I32` instruction, it is possible to fold it if `%0` is a
`CONST_I32` from an immediate number. But in this case it is a global
address, so we shouldn't do that. But we haven't checked if the operand
of `ADD` is an immediate so far. This fixes the problem. (The case
applies the same for `ADD_I64` and `CONST_I64` instructions.)

Fixes https://bugs.llvm.org/show_bug.cgi?id=47944.

Patch by Julien Jorge (jjorge@quarkslab.com)

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D90577